Someone who unsubscribes is added to the unsubscribe list and excluded from every future campaign automatically. Nobody has to remember, and no mailing list can accidentally include them.
Adding an address yourself
Use manually add email address when someone asks you directly — by phone, by reply, in person — rather than clicking the link. Honour it the same day. If the address is already on the list you are told, and nothing is duplicated.
Removing an address
ALMOST NEVER DO THIS
Reading the number
A steady trickle of unsubscribes is healthy — it is a list cleaning itself. A spike after one campaign is a message about that campaign: too frequent, the wrong audience, or content people did not sign up for.
AN UNSUBSCRIBE IS NOT A LOST CUSTOMER
They have stopped receiving marketing, not stopped buying. They remain a contact, and your reps can still talk to them — this list governs bulk email, not the relationship.